feat(fabric): coalesce a split agent turn into ONE message (deterministic)

OpenClaw delivers an agent turn whose blocks are text -> thinking/tool
-> text via multiple inbound deliver() calls (a non-text block is a
delivery boundary), so one turn became N Fabric messages.

Fix: buffer deliver() segments per channel (src/coalesce.ts) and flush
them as ONE postMessage at a deterministic boundary — the finally after
dispatchInboundReplyWithBase() resolves, which provably runs only after
every deliver() of the turn (verified: deliver,deliver -> dispatch
returned -> flush). No hooks, no timers, no idle guessing. The
agent_end hook was rejected: it fires BEFORE deliver(). gateway_stop
flushes any leftover; a long safety timeout is a leak-guard only.
channels.fabric.coalesce=false restores raw per-segment posting.

Verified on local openclaw + Fabric with a fake text/thinking/text
model: single trigger -> exactly one merged message.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

index.ts

@@ -6,6 +6,7 @@
 import { defineChannelPluginEntry } from 'openclaw/plugin-sdk/core';
 import type { OpenClawPluginApi } from 'openclaw/plugin-sdk/core';
 import { fabricChannelPlugin } from './src/channel.js';
+import { flushAllFabric } from './src/coalesce.js';
 import { FabricInbound } from './src/inbound.js';
 import { listEnabledFabricAccounts } from './src/accounts.js';
 import { registerFabricTools } from './src/tools.js';
@@ -37,7 +38,7 @@ export default defineChannelPluginEntry({
       config?: unknown;
       pluginConfig?: { identityFilePath?: string };
       logger: { info: (m: string) => void; warn: (m: string) => void };
-      on: (ev: string, fn: () => void) => void;
+      on: (ev: string, fn: (...args: unknown[]) => unknown) => void;
       registerTool: (d: unknown) => void;
     };
     const cfg = (api.config ?? {}) as { channels?: { fabric?: { centerApiBase?: string } } };
@@ -86,7 +87,12 @@ export default defineChannelPluginEntry({
       void syncFabricCommands(client, cfg, accounts, api.logger);
     });
 
+    // Note: the per-turn coalesce flush happens deterministically in
+    // inbound.ts right after dispatchInboundReplyWithBase resolves (that
+    // is the real "all deliveries done" boundary; the agent_end hook fires
+    // BEFORE deliver()). gateway_stop only flushes any leftover buffer.
     api.on('gateway_stop', () => {
+      void flushAllFabric();
       inbound?.stop();
       inbound = null;
     });